It’s only true is the car goes exactly 51.1 miles. Environmental Economics crunched the numbers. NPR agrees.

For a trip of 50 miles, the Volt gets 250 miles per gallon. But, for a trip of 200 miles, the Volt gets 62.5 mpg. Based on the EPA decision to rate the Volt at 230 mpg, they are assuming a trip of 51.11 miles.

Left unanswered: what is the EPA mppc (miles per pound of coal) for the Volt when running off the electric engine?

GM made a mistake by touting 230 mpg, a number they devised. Even EPA hasn’t agreed with it. I hope the Volt is a game changer, but GM has a long and tired history of doing innovative things on one hand, then screwing them up on the other. Plus, with a price starting at $40,000 and needing a minimum temperature between 32Â°F to 50Â°F to run on the battery alone,I wonder just how practical it is and how many will sell.

Left unanswered: what is the EPA mppc (miles per pound of coal) for the Volt when running off the electric engine?

Yep – that is the first question we asked when we saw the bit yesterday. If my local electric utillity burns coal – what is the offset for charging the car. Also, I may not have to buy gas as often – but what will it do to my electric bill to charge the car?

GM’s press release says it costs 40 cents per day to charge the Volt. I crunched numbers using an average cost of 12 cents per Kwh and came up with 1,217 Kwh/yr or 1,825 pounds of CO2 at the standard 1.5 pounds of CO2 per Kwh. This is obviously a shot in the dark, as we have no idea how GM came up with their 40 cent estimate, but it should be somewhere near ballpark. (A higher estimated cost per unit would lead to a lower total number of Kwh.)

Keep in mind, also, that most trips people make are short ones. DOT puts the mean trip length at 10 miles (http://www.bts.gov/publications/bts_special_report/2007_10_03/html/table_02.html), where Volt excels. Even on a 50-mile trip, Volt uses an estimated 3 Kwh and no gas. That’s 5 pounds CO2 compared to Prius’s 19 pounds. Even if you drive 100 miles at a time, your net fuel consumption would be (50*0) + (50*1/62.5)= 0.8 gallons + 3 Kwh. That still compares favorably with 1.9 gallons in the 2010 Prius. Volt would emit about 20 pounds of CO2 for the trip compared to Prius’s 38 pounds.

As the trip lengthens, the difference diminishes. The difference between 53 mpg and 62 mpg on a thousand mile trip is just 2.6 gallons (16.2 vs. 18.8), saving only 52 pounds of CO2 (324 vs. 376). So for long-haulers, the difference isn’t that significant. But for commuting, it’s pretty significant.

The price and the minimum temperature eliminates a lot of us from buying it (how do you get to work when the temp is -30?), but it’s still a step in the right direction.